DESCANT

The DESCANT neutron detector array consists of 70 close-packed hexagonal detectors filled with deuterated benzene. DESCANT can be mounted to either the TIGRESS or the GRIFFIN array. The former allows the neutron tagging of fusion evaporation reactions. In these reactions a radioactive ion beam delivered by ISAC-II impinge at energies between 1.5 and 15 MeV/nucleon on a thin foil. The beam particle can form an excited compound nucleus with the target particle which will de-excite via emission of neutrons, charged particles and/or γ-rays. Detecting the neutrons in DESCANT in coincidence with the detection of γ-rays in the TIGRESS array allows the selection of specific de-excitation channels. Using DESCANT together with the new GRIFFIN array allows the detection of delayed neutrons emitted in the β-decay of the low energy (30-60 keV) radioactive ion beams provided by the ISAC-I facility. DESCANT design, development, and installation was supported by an $2M New Initiatives Fund awarded by CFI in 2006 to the University of Guelph. The DESCANT spectrometer (Figure 1) is now fully commissioned and operational at ISAC.

 

In order to achieve a close-packed configuration the detectors have five different shapes, all hexagonal with varying degrees of asymmetry (figure 2). Each detector contains up to 2 liters of deuterated benzene scintillator (BC-537 from St. Gobain). The deuterated benzene can detect both recoiling electrons from Compton-scattered γ-rays and recoiling deuterons on which neutrons scattered. Due to the higher ionization density of the recoiling deuterons the delayed component of the scintillation light is larger for events caused by neutrons than for those caused by γ-rays. This can be used to distinguish between detected neutrons and γ-rays by performing a pulse-shape discrimination (PSD). The anode signals of the photomultipliers, that detect the scintillation light, are read out by digitizer cards built by the Université de Montréal. Each digitizer card has four channels of fast sampling analog-to-digital converters (ADCs) which are connected to FPGAs, providing energy, timing and pulse-shape discrimination information to the data acquisition system.